The present invention relates to a method to create without mechanical agitation a low shear low turbulence flow pattern within a continuous liquid phase contained in a vessel, by continuously or periodically injecting and preferably recycling a neutral immiscible lighter (less dense) fluid, preferably gas, below the free surface of the continuous phase. In one embodiment of the present invention the continuous liquid phase further comprises a dispersed phase which needs to be distributed within continuous phase without particle agglomeration or excessive (e.g. not more than 15%, preferably not more than 8%) breakup in order to either preserve or to slightly modify (reduce) the initial size distribution of the particles for subsequent batch processing.
There is a prior art relating to the injection of gas into a continuous liquid phase in sparging and, less often, surface aeration systems. Mechanically agitated tanks are usually used for this task and the main purpose of these systems is to disperse a gaseous component within a liquid component, (e.g. ethylene gas in liquid styrene) for further processing. Other applications involve high pressure gas injection to aid mechanical agitation/stirring by intensifying the mixing and increasing turbulence level in a stirred tank. All these systems operate in highly turbulent regimes and are equipped with mechanical agitators, (Wessner et al 2002, Nienow et al 1977, Nienow et al 1985a, Tatterson 1991, Bujalski 1988, Warmoeskerken et al 1984, Chapman et al 1983). There are also numerous applications of in situ gas injection to remediate contaminated aquifers or soil matrix, but they serve totally different purpose and operate on different principles than process described in the present invention.
The applicants have been unable to locate any art, which discloses the subject matter of the present invention (i.e. injection of an inert immiscible lighter or less dense fluid into a continuous liquid phase to create a low shear low turbulence, (preferably laminar), flow pattern within a continuous phase contained in a vessel. If the continuous phase optionally further comprises a dispersed phase, the present invention provides the mechanism to create, with no mechanical agitation, a laminar low shear flow pattern to suspend and to distribute, preferably relatively uniformly, the dispersed phase within a volume or a portion of the continuous phase, with minimum interaction between particles particularly during subsequent processing. The application of such a flow pattern can be useful in any process where the substrate (liquid or solid) is dispersed as a suspension or an emulsion or as a particle cloud in an immiscible continuous phase and the dispersed phase may be further batch processed or undergo a chemical reaction (e.g. polymerization) with the requirement to substantially (e.g. 90%, most preferably 95%) preserve or, optionally, to modify (decrease) (e.g. up to 15%, preferably 8% of the largest particle size) the initial size distribution.
In conventional processes, a phase to be processed, dispersed in a continuous liquid phase is usually subjected to some form of mechanical agitation. If the initial particle size distribution of the dispersed phase, which may have been obtained by any means including pressure atomization, extrusion, mechanical agitation, jet cutting or other means of disintegration, is to be maintained during further processing or chemical reaction, the agitation needs to produce low enough shear and low turbulence flow so as not to cause particles to agglomerate or not to cause further particle break up. With conventional mechanical agitation it is difficult to generate a low turbulence, uniform shear field as the velocity gradient along an agitator blade is a function of the liquid properties, the speed of rotation and the distance from the agitator shaft. Accordingly the shear is highly non-uniform and generally the level of turbulence is high and this tends to change the initial particle size distribution into a new, usually a normal, distribution of particle sizes.
The present invention seeks to provide a method of generating a low shear, low turbulence, in some applications preferably laminar, zone within a continuous liquid phase in a vessel, with no mechanical agitation. If dispersed particles are comprised in the continuous liquid they flow within this zone with minimum mutual interaction, remaining submerged and thoroughly (uniformly) distributed within the continuous liquid volume during subsequent processing. In such environment, the initial particle size distribution can be largely preserved or, optionally, the initial particle size distribution can be modified (e.g. slightly reduced) or improved by some controlled breakups of the largest particles. (e.g. the largest 10% of the particle size distribution).
Optionally, in one embodiment of the invention, the particle size distribution of the discontinuous phase may be reduced by causing a secondary breakup of the majority (at least 85%) of the particles or the droplets dispersed in the continuous phase.
The method can be applied in processes where density ratios between dispersed and continuous phases are higher and lower than 1 within the range of xc2x120%.
The present invention provides a process for creating a low shear flow pattern with a controlled low turbulence level, without mechanical agitation, in a continuous liquid phase contained a vessel, comprising continuously or periodically injecting into selected part(s) of the vessel one or more streams of fluid immiscible and inert to the vessel contents and having a density lower than the reactor contents, and retrieving this fluid above free surface of liquid phase and, preferably, reinjecting it back to the vessel.